JP4636825B2 - Image forming apparatus - Google Patents

Description

The present invention relates to an image forming apparatus and a process cartridge for an image forming apparatus employing the charging method by near discharge, it details a process speed faster, in which the cycle time required for printing is concerned short small imaging equipment.

  2. Description of the Related Art Conventionally, an image forming apparatus employing an electrophotographic process has a charging unit that charges the surface of a member to be charged (hereinafter referred to as a photoreceptor). One of the charging methods used in the charging means is a charging method using proximity discharge. In this method, the surface of the photosensitive member is charged by a proximity discharge generated by bringing a charging member provided in the charging device into contact with the surface of the photosensitive member or by bringing the charging member close to the surface without contact.

  In recent years, high image quality and miniaturization of devices are increasingly desired, and charging devices are also required to have high image quality and miniaturization. In order to solve such a problem, a charging device using a so-called proximity discharge method in which a charging member is used to discharge in contact with or close to the photosensitive member is effective because it does not require a large charging device.

  However, it has been found that the charging method using proximity discharge deteriorates the surface of the photoconductor because the discharge concentrates near the surface of the photoconductor. Unlike the deterioration due to mechanical rubbing, the deterioration of the surface of the photoreceptor due to the proximity discharge occurs even when there is no contact member on the photoreceptor.

  For example, FIG. 1 shows an example in which the deterioration state of the photoreceptor surface due to proximity discharge is examined. In this example, only the charging member is placed close to the surface of the photoconductor in a non-contact state, and when the charging experiment is performed by running for about 150 hours continuously, the change in film thickness of the photoconductor surface, that is, the amount of film scraping is measured. The results are shown.

  The photoconductor used in the experiment is an organic photoconductor using polycarbonate as the charge transport layer, and all the members contacting the photoconductor are removed, and a non-contact charging roller to which a voltage in which an AC bias is superimposed on a DC bias is applied. Was used for charging. As a result, it was found that the amount of abrasion of the film on the surface of the photoconductor gradually increased with the run time, and the film thickness of the photoconductor gradually decreased. The mechanism of film thickness reduction is not currently clarified during the examination. However, analysis of a photoreceptor with a reduced film thickness revealed that the polycarbonate constituting the photoreceptor was decomposed, such as carboxylic acid. was detected. As described above, since the substance that is considered to have decomposed the components constituting the photoconductor was detected by the proximity discharge, the following may be considered as a mechanism for reducing the film thickness of the photoconductor. This will be described with reference to FIG.

FIG. 2 is a schematic diagram for explaining an initial surface state (a) and a deteriorated state (b) of the photosensitive member 1 when the charging roller 2a and the photosensitive member surface are opposed to each other with a minute gap and are subjected to proximity discharge. is there.
That is, when proximity discharge is performed, energy of particles (for example, ozone, electrons, excited molecules, ions, plasma, etc.) generated by the discharge is irradiated to the charge transport layer 1a on the surface of the photoreceptor in the discharge region on the surface of the photoreceptor. . This energy is resonated and absorbed by the binding energy of the molecules constituting the surface of the photoreceptor, and as shown in FIG. 2A, the charge transport layer 1a has a reduced molecular weight due to the breakage of the resin molecular chain and the degree of entanglement of the polymer chain. Chemical degradation such as lowering of resin and evaporation of resin. It is considered that the film thickness of the charge transport layer 1a on the surface of the photoreceptor gradually decreases due to such chemical deterioration of the photoreceptor due to the proximity discharge.

As described above, in addition to the countermeasure against the film thickness reduction due to mechanical rubbing, which has been conventionally taken, a countermeasure against the film thickness reduction due to the chemical deterioration of the photoreceptor surface caused by the proximity discharge is necessary. I understood that.
The decrease in the film thickness on the surface of the photoreceptor due to the proximity discharge is considered to occur due to the energy of the particles generated by the discharge. Therefore, it is considered that the reduction occurs not only in the exemplified polycarbonate but also in the case where a photoreceptor of another material is used.

The following measures have been taken so far to prevent a decrease in film thickness on the surface of the photoreceptor. For example, there is a photoconductor whose surface is coated with amorphous silicon carbide to improve wear resistance. Further, for example, an organic photoreceptor in which an inorganic material such as alumina is dispersed in a charge transport (CTL) layer on the surface of the photoreceptor to improve wear resistance is used (for example, Patent Document 1, Patent Document). 2).
However, with such a configuration, durability against mechanical wear can be improved, but chemical deterioration of the surface of the photoreceptor due to proximity discharge cannot be prevented.

  For the purpose of reducing the coefficient of friction of the surface of the photoreceptor, it has been proposed to include means for applying zinc stearate to the surface of the photoreceptor (see, for example, Patent Document 3 and Patent Document 4). In addition, in order to improve the problem that foreign matter easily adheres to the surface of the photoconductor, it has been proposed to include means for applying zinc stearate to the surface of the photoconductor (see, for example, Patent Document 5 and Patent Document 6). .

Zinc stearate has a low coefficient of friction as a general effect and is used as a lubricant. When it is applied to the surface of a photoreceptor belt, it improves releasability, improves development background stains, and improves transfer efficiency. Is known, and certain effects are expected in each of the above proposals.
However, none of these proposals has been optimized as a measure for dealing with the decrease in the film thickness of the photosensitive member, which is a problem in the proximity discharge as in the present invention, and in particular, the cycle time required for high-speed processes and printing is short. Not enough to handle the process.

  Further, in recent years, image forming apparatuses are required to cope with higher speeds, such as progress in process technology and speeding up of color machines, and the technology of photoconductors has been advanced toward longer life. On the other hand, the higher the speed of the photoconductor and the shorter the cycle time, that is, the so-called time (second) per cycle of the printing process, the greater the torque that drives the photoconductor, that is, the mechanical load. Here, one cycle of the printing process refers to a cycle required for printing such as charging-developing-transfer-fixing-cleaning. In the following, the shortening of the cycle time may be abbreviated as a small cycle time.

  In high-temperature and high-humidity environments, the torque increases to increase the power supply capacity of the drive motor, or when the cleaning member is in contact, especially due to environmental dependence, or the member is damaged or turned up due to an increase in frictional force. Happens. The turn is mainly of a blade shape. The tendency becomes more prominent as the high durability drum has less wear.

High speed here means that the speed of a series of printing processes is high. The linear velocity generally refers to a process speed (paper conveyance speed).
The printing process includes charging the photosensitive member, forming a latent image by exposure, developing the toner image on the latent image, transferring the toner image to a printing medium such as paper / intermediate transfer member, and removing residual toner on the photosensitive member. Refers to a series of flows, such as cleaning and, if necessary, charge removal of the object. The print medium on which the toner has been transferred is output outside the apparatus after the toner has been fixed.

In order to cope with such high speed, it has been proposed to include a polymer containing a siloxane unit as a binder resin for the surface layer (see, for example, Patent Document 7).
However, according to the inventor's experiment, the sustainability of the torque reduction effect is low, and it is not sufficient from the viewpoint of effectiveness and ease of use, such as providing specific provisions for the charging width and transfer width.

As described above, in order to cope with uniformity and stability of charging and high speed, the photosensitive member and the charging member for applying a voltage including an alternating current component provided in contact with or close to the photosensitive member are provided. was the charging device, a high speed / but be used in an image forming apparatus adapted to process a small cycle time is indispensable at present for such request, not the image forming equipment is obtained satisfactory is the current situation.

JP 2002-207308 A JP 2002-229227 A JP 2002-55580 A JP 2002-244487 A JP 2002-244516 A JP 2002-156877 A JP 2002-229301 A

The present invention has been made in view of the above prior art, and in an image forming apparatus employing a charging method using proximity discharge, it is possible to prevent deterioration of the surface of the photoreceptor due to proximity discharge, has good durability in the process of high-speed / low cycle time is required in the print process one cycle per time, and provide an image forming equipment which enables forming an image generation blade inversion or abnormal image is not stable The purpose is to do.

The photosensitive member as a member to be charged used in the present invention is also intended for commonly used ones including a conductive layer and a support. Therefore, it is necessary to cope with the following problems.
When a normal resin is used as the surface layer of the photoconductor as a constituent layer of the photoconductor, the frictional force with the member in contact with the photoconductor increases as the process speed of the photoconductor increases and the cycle time decreases. Therefore, the torque for driving the photoconductor increases. When the driving force becomes insufficient with respect to the increased torque, driving unevenness occurs and an image is abnormal. Further, when the torque increase is significant, the contact member may be damaged, and the image forming apparatus may not operate normally.

  When the member that cleans the transfer residual toner is a cleaning blade, the blade is broken, that is, chipped, appears as a streak on the image, or the blade cannot support the frictional force with the photoreceptor. The blade is turned over, and the operation necessary for the image forming apparatus cannot be performed.

  The increase in frictional force is caused not only by a process speed increase and a cycle time decrease, but also by a hazard due to charging. Such a phenomenon is more likely to occur in contact charging and proximity charging than in scorotron charging, and is considered to be related to deterioration of the surface of the photoreceptor due to charging. That is, it has been observed that the frictional force with the blade becomes extremely high due to the oxidation and decomposition of the surface constituent material due to charging. When charging is performed by applying a voltage including so-called alternating current in which alternating current is superimposed on direct current, the surface deterioration is further increased and the frictional force is further increased.

  The present inventors have intensively studied to solve the above problem, and first, as a measure not to cause a reduction in the film thickness of the photosensitive member, which is a problem in the proximity discharge, a protective substance may be interposed in a necessary amount of discharge region. By obtaining knowledge that it is necessary and using this as a base, in the process of high speed / small cycle time, the protective material is present on the surface of the photoconductor in an appropriate amount corresponding to the discharge conditions. It was possible to impart a lubricating action while protecting the photoconductor, and found that the above problems could be solved, leading to the present invention. Hereinafter, the present invention will be specifically described.

That is , the present invention provides a moving photosensitive member, a protective substance coating device that supplies a protective substance while abutting and moving on the surface of the photosensitive member, and a contact member in close proximity to the photosensitive member. A charging device including a charging member that charges the photosensitive member by discharging due to application of a voltage, an exposure device that forms an electrostatic latent image on the surface of the charged photosensitive member, and the formed electrostatic latent image with toner. An image forming apparatus including at least a developing device for developing,
The photoreceptor includes a photosensitive layer in which a charge transport layer and a charge generation layer are laminated in order from the surface side,
The charge transport layer comprises polycarbonate;
The protective substance is zinc stearate , and the amount of metal element ratio (%) measured by XPS of the fatty acid metal salt present on the surface of the photoreceptor in the discharged region is obtained by the following formula (4). The image forming apparatus is characterized in that the cycle time required for printing on the photosensitive member is less than 0.60 seconds / cycle.
1.52 × 10 ⁻⁴ × [Vpp− (2 × Vth)] × (f / v) (4)

In the above formula, Vpp is the amplitude (V) of the AC component applied to the charging member, f is the frequency (Hz) of the AC component applied to the charging member, and v is the moving speed (mm / mm) of the photosensitive member surface facing the charging member. sec), Vth is a discharge starting voltage (V) is the table, the Vpp satisfies 2200 ≦ Vpp ≦ 3000, and the f satisfies 500 ≦ f ≦ 4000.
Here, the value of Vth is as follows: the film thickness of the photoconductor is d (μm), the relative dielectric constant of the photoconductor is εopc, the closest distance (μm) between the charging member surface and the surface of the photoconductor is Gp, and the photoconductor is charged. When the relative dielectric constant in the space between the members is εair, the following formula (2):
Vth = 312 + 6.2 × (d / εopc + Gp / εair) + (7737.6 × d / εopc) ^1/2 (2)
Calculated from

Further, in the image forming apparatus of the present invention, the amount of the metal element ratio (%) measured by XPS of the fatty acid metal salt present on the surface of the photoreceptor in the discharged region is obtained by the following formula (5). It is preferable that it is more than the amount.
2.22 × 10 ⁻⁴ × [Vpp− (2 × Vth)] × (f / v) (5)

In the above formula, Vpp is the amplitude (V) of the AC component applied to the charging member, f is the frequency (Hz) of the AC component applied to the charging member, and v is the moving speed (mm / mm) of the photosensitive member surface facing the charging member. sec), Vth represents the discharge start voltage (V).
Here, the value of Vth is as follows: the film thickness of the photoconductor is d (μm), the relative dielectric constant of the photoconductor is εopc, the closest distance (μm) between the charging member surface and the surface of the photoconductor is Gp, and the photoconductor is charged. When the relative dielectric constant in the space between the members is εair, the following formula (2):
Vth = 312 + 6.2 × (d / εopc + Gp / εair) + (7737.6 × d / εopc) ^1/2 (2)
Calculated from

  Furthermore, in any of the image forming apparatuses of the present invention, it is preferable that a cycle time required for the printing is less than 0.44 seconds / cycle.

  Furthermore, in any of the image forming apparatuses according to the present invention, it is preferable that the linear movement speed of the photosensitive member is different from the linear movement speed of the protective material coating device that contacts the photosensitive member.

  Adopting the charging method by proximity discharge according to the present invention, the amount of the total element ratio (%) measured by XPS of the protective substance present on the surface of the photoreceptor in the discharged region is set as the amplitude of the AC component applied to the charging member. By using the appropriate relationship based on the relationship between the frequency, the moving speed of the photoconductor surface, and the discharge start voltage, the photoconductor surface is prevented from being deteriorated due to the proximity discharge, and is highly durable. In addition to providing an image forming apparatus that enables stable image formation without occurrence of a crack, an increase in torque is suppressed and damage to a cleaning member or the like is prevented even in a high-speed process electrophotographic apparatus with a small cycle time. In addition, it is possible to provide an electrophotographic apparatus and a process cartridge in which the diameter, size, cost, and durability of the electrophotographic photosensitive member are achieved. In particular, the above-described effect is further exhibited when the cycle time is less than 0.60 seconds / cycle, preferably less than 0.44 seconds / cycle.

Embodiment 1
Hereinafter, an image forming apparatus to which the present invention is applied will be described with reference to Embodiment 1. However, aspects of the present invention are not limited thereto. FIG. 3 shows an example of an image forming apparatus having a configuration common to the embodiments described later. This image forming apparatus includes a photoreceptor 1 as a member to be charged made of an organic photoreceptor.

  In FIG. 3, the photosensitive member 1 is driven to rotate by a driving device (not shown), and the surface thereof is predetermined by a rotatable roller-shaped charging member (hereinafter referred to as a charging roller) 2a provided in a charging device 2 of a proximity charging system. Charged to the polarity of. The charged surface of the photoreceptor 1 is exposed by the exposure device 3 to form an electrostatic latent image corresponding to the image information. The electrostatic latent image is developed with toner as a developer supplied from the developing device 4 to the surface of the photoreceptor 1 to be visualized as a toner image.

  On the other hand, a transfer sheet as a recording medium is fed toward the photosensitive member 1 from a sheet feeding unit (not shown). A toner image on the photoconductor 1 is transferred onto the transfer paper on the transfer paper by a transfer device 5 disposed opposite to the photoconductor 1. The transfer paper onto which the toner image has been transferred is separated from the photoreceptor 1 and then conveyed to the fixing device 6 along the transfer material conveyance path 10 to fix the toner image. Transfer residual toner (not shown) remaining on the photosensitive member 1 after the toner image is transferred to the transfer paper is removed from the photosensitive member 1 by the cleaning device 8.

  Further, the residual charge on the surface of the photoconductor after the transfer residual toner is removed is removed by the static eliminator 9. In this way, the photoreceptor 1 is used repeatedly. Note that the image forming apparatus according to the present exemplary embodiment includes the protective substance coating apparatus 30, which will be described in detail later.

  In the image forming apparatus according to the present embodiment, the photosensitive member 1, the charging device 2 including the charging roller 2a, the developing device 4, the protective substance coating device 30, and the cleaning device 8 are integrally configured and detached from the image forming apparatus main body. It is configured as a possible process cartridge. Since such process cartridges are replaced together, it is easy to set the amount of the protective substance contained in the protective substance coating apparatus 30 and the initial film thickness of the photosensitive member to an appropriate amount. Is suitable.

  In the image forming apparatus according to the present embodiment, the process cartridge is configured as described above. However, the process cartridge is not limited to this, and the charging device including the photosensitive member 1 and the charging roller 2a according to the image forming apparatus. At least any one device selected from the device 2 and the protective substance coating device 30 may be configured integrally.

  Next, the charging device 2 used in the image forming apparatus according to the first embodiment will be described. The charging device 2 charges the photoreceptor 1 using proximity discharge. As a method of charging the photosensitive member 1 using proximity discharge, a contact charging method in which a rotatable roller-shaped charging roller 2 a is disposed in contact with the photosensitive member 1, and the charging roller 2 a is not in contact with the photosensitive member 1. And a non-contact charging method. Although the present invention can also be applied to a contact charging method, the first embodiment uses a non-contact charging method.

  In the contact charging method, it is preferable to use an elastic member that improves the contact property with the surface of the photoreceptor and does not apply mechanical stress to the photoreceptor 1. However, when an elastic member is used, the charging nip width is widened, which may cause the protective material to easily adhere to the charging roller 2a side. For this reason, it is more advantageous to adopt a non-contact charging method for high durability.

FIG. 4 is a schematic configuration diagram for explaining an example of the charging device 2 used in the image forming apparatus according to the first embodiment.
In the first embodiment, as shown in FIG. 4, a non-contact charging method in which the charging roller 2 a is disposed so as to face at least the image forming area 11 on the surface of the photoreceptor with a predetermined charging gap 14 is employed.

  The charging roller 2a includes a shaft portion 21a and a roller portion 21b. The roller portion 21 b can be rotated by the rotation of the shaft portion 21 a, and a portion of the surface of the photoreceptor 1 that faces the image forming region 11 where an image is formed is not in contact with the photoreceptor 1. The length of the charging roller, that is, the dimension in the axial direction is set slightly longer than the image forming area, and spacers 22 are provided at both ends in the longitudinal direction. These two spacers are brought into contact with the non-image forming regions 12 at both ends of the surface of the photoconductor to form a minute gap 14 between the photoconductor 1 and the charging roller. The minute gap 14 is configured such that the distance at the closest portion between the charging roller and the photosensitive member 1 can be maintained at 5 to 100 μm.

  A more preferable range of the gap 14 is 30 to 65 μm. In the apparatus according to the first embodiment, the gap 14 is set to 50 μm. Further, the shaft portion 21a is pressed against the photosensitive member side by a pressing spring 15 made of a spring. Thereby, the minute gap 14 can be accurately maintained. Further, the charging roller rotates along with the surface of the photoreceptor via the spacer 22.

  A charging power source 16 is connected to the charging roller 2a. As a result, the surface of the photoconductor is uniformly charged by proximity discharge in a minute gap between the surface of the photoconductor and the surface of the charging roller. In the first embodiment, the applied voltage is an alternating voltage obtained by superimposing an AC voltage that is an AC component on a DC voltage that is a DC component. That is, a voltage including an AC component is applied. When an alternating voltage obtained by superimposing an AC voltage on a DC voltage is applied as an applied voltage to the charging roller 2a, influences such as variations in charging potential due to minute gap fluctuations are suppressed, and uniform charging becomes possible.

  The charging roller 2a has a cored bar as a conductive support having a cylindrical shape and a resistance adjusting layer formed on the outer peripheral surface of the cored bar. The surface of the charging roller 2a is preferably hard. A rubber member can also be used as the roller member, but if it is a member that is easily deformed, such as a rubber member, it is difficult to maintain a uniform small gap 14 between the photosensitive member 1 and the central portion of the charging roller 2a depending on image forming conditions. There is a possibility that only the surface of the photoconductor suddenly contacts. Since it is difficult to cope with the disturbance of the protective material caused by local / sudden contact of the charging roller 2a with the surface of the photoreceptor, a hard member with less deflection is used when using the non-contact charging method. desirable.

  Specific examples of the charging roller 2a having a hard surface include, for example, a thermoplastic resin composition (for example, polyethylene, polypropylene, polymethyl methacrylate, polystyrene, and a copolymer thereof) in which a polymer type ion conductive agent is dispersed. The resistance adjusting layer is used to form a surface, and the surface thereof is cured with a curing agent. The cured film treatment is performed, for example, by immersing the resistance adjustment layer in a treatment solution containing an isocyanate-containing compound, but may be performed by forming a cured treatment film layer on the surface of the resistance adjustment layer. In this embodiment, the charging roller 2a is formed with a diameter of φ10 mm.

The photoreceptor 1 of the present embodiment is obtained by providing a photosensitive layer on a conductive support.
Examples of the conductive support include those having a volume resistance of 10 ¹⁰ Ω · cm or less, such as metals such as aluminum, nickel, chromium, nichrome, copper, gold, silver, and platinum, tin oxide, and indium oxide. Metal oxide coated with film or cylindrical plastic or paper by vapor deposition or sputtering, or a plate made of aluminum, aluminum alloy, nickel, stainless steel, etc., and methods such as extrusion or drawing After forming the tube, it is possible to use a tube surface-treated by cutting, superfinishing, polishing, or the like. Further, for example, endless nickel belts and endless stainless steel belts disclosed in JP-A-52-36016 can also be used as the conductive support.

  In addition, those obtained by dispersing and coating conductive powder in an appropriate binder resin on the conductive support can also be used as the conductive support of the present invention. Examples of the conductive powder include carbon black, acetylene black, metal powder such as aluminum, nickel, iron, nichrome, copper, zinc and silver, or metal oxide powder such as conductive tin oxide and ITO. It is done.

  The binder resin used simultaneously is polystyrene, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, styrene-maleic anhydride copolymer, polyester, polyvinyl chloride, vinyl chloride-vinyl acetate copolymer. , Polyvinyl acetate, polyvinylidene chloride, polyarylate, phenoxy resin, polycarbonate, cellulose acetate resin, ethyl cellulose resin, polyvinyl butyral, polyvinyl formal, polyvinyl toluene, poly-N-vinylcarbazole, acrylic resin, silicone resin, epoxy resin, melamine Examples thereof include thermoplastic, thermosetting resins, and photocurable resins such as resins, urethane resins, phenol resins, and alkyd resins. Such a conductive layer can be provided by dispersing and coating these conductive powder and binder resin in a suitable solvent such as tetrahydrofuran, dichloromethane, methyl ethyl ketone, and toluene.

  Furthermore, a heat-shrinkable tube in which the conductive powder is contained in a material such as polyvinyl chloride, polypropylene, polyester, polystyrene, polyvinylidene chloride, polyethylene, chlorinated rubber, and Teflon (registered trademark) on a suitable cylindrical substrate. Those provided with a conductive layer can also be favorably used as a conductive support for the photoreceptor in the present invention.

Next, the photosensitive layer will be described. The photosensitive layer may be a single layer or a laminated layer. For convenience of explanation, the photosensitive layer is first described from the case where it is composed of a charge generation layer and a charge transport layer.
The charge generation layer is a layer mainly composed of a charge generation material. Known charge generation materials can be used for the charge generation layer, and representative examples thereof include monoazo pigments, disazo pigments, trisazo pigments, perylene pigments, perinone pigments, quinacridone pigments, quinone condensed polycyclic compounds, Squalic acid dyes, other phthalocyanine pigments, naphthalocyanine pigments, azulenium salt dyes and the like are used. These charge generation materials may be used alone or in combination of two or more.
For the charge generation layer, the charge generation material is dispersed in a suitable solvent together with a binder resin as necessary using a ball mill, attritor, sand mill, ultrasonic wave, etc., and this is applied onto a conductive support and dried. It is formed by doing.

  As the binder resin used for the charge generation layer as necessary, polyamide, polyurethane, epoxy resin, polyketone, polycarbonate, silicone resin, acrylic resin, polyvinyl butyral, polyvinyl formal, polyvinyl ketone, polystyrene, polysulfone, poly-N- Vinyl carbazole, polyacrylamide, polyvinyl benzal, polyester, phenoxy resin, vinyl chloride-vinyl acetate copolymer, polyvinyl acetate, polyphenylene oxide, polyamide, polyvinyl pyridine, cellulose resin, casein, polyvinyl alcohol, polyvinyl pyrrolidone, etc. It is done. The amount of the binder resin is suitably 0 to 500 parts by weight, preferably 10 to 300 parts by weight with respect to 100 parts by weight of the charge generating material. The binder resin may be added before or after dispersion.

  Examples of the solvent used here include isopropanol, acetone, methyl ethyl ketone, cyclohexanone, tetrahydrofuran, dioxane, ethyl cellosolve, ethyl acetate, methyl acetate, dichloromethane, dichloroethane, monochlorobenzene, cyclohexane, toluene, xylene, and ligroin. In particular, ketone solvents, ester solvents, and ether solvents are preferably used. These may be used alone or in combination of two or more.

The charge generation layer is mainly composed of a charge generation material, a solvent, and a binder resin, and any additive such as a sensitizer, a dispersant, a surfactant, or silicone oil may be contained therein. Good.
As a coating method for the coating solution, a dip coating method, spray coating, beat coating, nozzle coating, spinner coating, ring coating, or the like can be used.
The thickness of the charge generation layer is suitably about 0.01 to 5 μm, preferably 0.1 to 2 μm.

  The charge transport layer can be formed by dissolving or dispersing a charge transport material and a binder resin in an appropriate solvent, and applying and drying the solution on the charge generation layer. Further, if necessary, two or more kinds of plasticizers, leveling agents, antioxidants and the like can be added. Charge transport materials include electron transport materials and hole transport materials.

  Examples of the electron transport material include chloroanil, bromanyl, tetracyanoethylene, tetracyanoquinodimethane, 2,4,7-trinitro-9-fluorenone, 2,4,5,7-tetranitro-9-fluorenone, 2, 4,5,7-tetranitroxanthone, 2,4,8-trinitrothioxanthone, 2,6,8-trinitro-4H-indeno [1,2-b] thiophen-4-one, 1,3,7- Examples thereof include electron-accepting substances such as trinitrodibenzothiophene-5,5-dioxide and benzoquinone derivatives.

  Examples of hole transport materials include poly-N-vinylcarbazole and derivatives thereof, poly-γ-carbazolylethyl glutamate and derivatives thereof, pyrene-formaldehyde condensates and derivatives thereof, polyvinylpyrene, polyvinylphenanthrene, polysilane, oxazole derivatives, Oxadiazole derivatives, imidazole derivatives, monoarylamine derivatives, diarylamine derivatives, triarylamine derivatives, stilbene derivatives, α-phenylstilbene derivatives, benzidine derivatives, diarylmethane derivatives, triarylmethane derivatives, 9-styrylanthracene derivatives, pyrazolines Derivatives, divinylbenzene derivatives, hydrazone derivatives, indene derivatives, butadiene derivatives, pyrene derivatives, bisstilbene derivatives, enamine derivatives, etc. Other known materials may be used. These charge transport materials may be used alone or in combination of two or more.

  As the binder resin, polystyrene, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, styrene-maleic anhydride copolymer, polyester, polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, polyvinyl acetate, Polyvinylidene chloride, polyarylate resin, phenoxy resin, polycarbonate, cellulose acetate resin, ethyl cellulose resin, polyvinyl butyral, polyvinyl formal, polyvinyl toluene, poly-N-vinyl carbazole, acrylic resin, silicone resin, epoxy resin, melamine resin, urethane resin And thermoplastic or thermosetting resins such as phenol resins and alkyd resins.

  The amount of the charge transport material is appropriately 20 to 300 parts by weight, preferably 40 to 150 parts by weight, based on 100 parts by weight of the binder resin. The thickness of the charge transport layer is preferably 25 μm or less from the viewpoint of resolution and responsiveness. The lower limit is preferably 5 μm or more, although it varies depending on the system used, particularly the charging potential.

  As the solvent used here, tetrahydrofuran, dioxane, toluene, dichloromethane, monochlorobenzene, dichloroethane, cyclohexanone, methyl ethyl ketone, acetone and the like are used. These may be used alone or in combination of two or more.

  The present invention can also be applied to a photoreceptor having a single-layer photosensitive layer. As such a photoreceptor, a photoreceptor in which the above-described charge generating material is dispersed in a binder resin can be used. The photosensitive layer can be formed by dissolving or dispersing a charge generating substance, a charge transporting substance, and a binder resin in a suitable solvent, and applying and drying them. Further, it is desirable to contain a plasticizer, a leveling agent, an antioxidant, particularly a hindered phenol compound or a hindered amine compound, if necessary.

  As the binder resin, in addition to the binder resin previously mentioned in the charge transport layer, the binder resin mentioned in the charge generation layer may be mixed and used. Of course, the polymer charge transport materials mentioned above can also be used favorably. The amount of the charge generating material with respect to 100 parts by weight of the binder resin is preferably 5 to 40 parts by weight, and the amount of the charge transporting material is preferably 0 to 190 parts by weight, and more preferably 50 to 150 parts by weight.

  The photosensitive layer is formed by dip coating, spray coating, bead coating, a coating solution in which a charge generating material and a binder resin are dispersed together with a charge transporting material using a solvent such as tetrahydrofuran, dioxane, dichloroethane, and cyclohexane. It can be formed by coating with a ring coat or the like. The film thickness of the photosensitive layer is suitably about 5 to 25 μm.

  In the photoreceptor of the present invention, an undercoat layer can be provided between the conductive support and the photosensitive layer. In general, the undercoat layer is mainly composed of a resin. However, considering that the photosensitive layer is coated with a solvent on these resins, the resin may be a resin having high solvent resistance with respect to a general organic solvent. desirable. Examples of such resins include water-soluble resins such as polyvinyl alcohol, casein, and sodium polyacrylate, alcohol-soluble resins such as copolymer nylon and methoxymethylated nylon, polyurethane, melamine resin, phenol resin, alkyd-melamine resin, and epoxy. Examples thereof include a curable resin that forms a three-dimensional network structure such as a resin. Further, a metal oxide fine powder pigment exemplified by titanium oxide, silica, alumina, zirconium oxide, tin oxide, indium oxide and the like may be added to the undercoat layer in order to prevent moire and reduce residual potential.

These undercoat layers can be formed using an appropriate solvent and a coating method like the above-mentioned photosensitive layer. Furthermore, a silane coupling agent, a titanium coupling agent, a chromium coupling agent, or the like can be used as the undercoat layer of the present invention. In addition, the undercoat layer in the present invention includes an anodized layer of Al ₂ O ₃ , an organic material such as polyparaxylylene (parylene), SiO ₂ , SnO ₂ , TiO ₂ , ITO, CeO _2. A material provided with an inorganic material such as a vacuum thin film can also be used favorably. In addition, known ones can be used. The thickness of the undercoat layer is suitably from 0 to 5 μm.

  Further, it is possible to provide a protective layer on the outermost surface layer of the photosensitive member, which is effective in improving the wear resistance. For example, in order to improve the wear resistance, a photoreceptor whose surface is coated with amorphous silicon, an organic photoreceptor provided with an outermost surface layer in which alumina, tin oxide or the like is further dispersed on the surface of the charge transport layer, or It is also possible to use a photoconductor provided with an acrylic or silsesquioxane-based crosslinked protective layer.

  As described above, the configuration of the photoreceptor 1 that can be used in the present invention is not limited to a specific configuration. A single layer configuration in which only a photosensitive layer mainly composed of a charge generation material and a charge transport material is provided on a conductive support, or a charge generation layer and a charge mainly composed of a charge generation material on a conductive support. A structure in which a charge transport layer mainly composed of a transport material is laminated, or a photosensitive layer mainly composed of a charge generation material and a charge transport material is provided on a conductive support, and a protective layer is further provided on the surface of the photosensitive layer. A charge generation layer mainly composed of a charge generation material and a charge transport layer mainly composed of a charge transport material are laminated on a conductive support, and a protective layer is further formed on the charge transport layer. A charge transport layer mainly composed of a charge transport material and a charge generation layer mainly composed of a charge generation material are laminated on the provided structure or a conductive support, and a protective layer is further formed on the charge generation layer. The present invention can be applied to a photoreceptor having various layer configurations such as a provided configuration.

According to the study by the present inventors, it has been found that when proximity discharge is used as the charging device, the surface of the photoreceptor is deteriorated. It has been found that this deterioration occurs because the surface of the photoconductor is directly exposed to the proximity discharge, and occurs even when there is no contact member on the surface of the photoconductor.
That is, it has been found that the photoreceptor surface deterioration due to proximity discharge occurs by a mechanism different from mechanical rubbing. Therefore, in the present embodiment, as a feature thereof, a protective substance coating apparatus is provided as a discharge deterioration preventing means for preventing the photoreceptor surface deterioration due to the proximity discharge. Details of the specific configuration will be described below.

  In the image forming apparatus of this embodiment, as shown in FIG. 3, a protective substance coating device 30 is provided as means for supplying the protective substance 32 to the moving photoreceptor surface. This protective substance coating device 30 has a fur brush 31 as a coating member, a protective substance 32, and a pressure spring 33 for pressing the protective substance in the fur brush direction. The protective material 32 is a solid protective material molded into a bar shape. The fur brush 31 is in contact with the surface of the photosensitive member 1, and is rotated around the shaft to pump up the protective substance 32 while scraping off the protective substance 32, and is carried on the brush to a contact position with the surface of the photosensitive member. Then, it is applied to the surface of the photoreceptor and supplied.

  Further, even if the protective material 32 is scraped off by the fur brush 31 with the passage of time, the protective material 32 is pressed against the fur brush 31 with a predetermined pressure by the pressurizing spring 33 so as not to contact the fur brush 31. Has been. As a result, the fur brush 31 is always uniformly pumped even if a small amount of the protective substance 32 is present.

In addition, there is a method of transferring the protective material 32 to the surface of the photoconductor by adding or externally adding the protective material 32 to the toner, but in that case, the amount of the protective material 32 on the surface of the photoconductor is determined depending on the image density or image pattern. Unevenness is likely to occur, and it is necessary to apply more protective material than necessary to compensate for this. By directly applying and supplying the protective material 32 to the surface of the photoconductor as in this embodiment, the protective material can be stably distributed on the surface of the photoconductor without changing depending on various conditions such as image density and image pattern. Can do.
Further, as will be described later, it is important that the protective material 32 is present in an appropriate amount on the surface of the photoreceptor 1, and means for supplying the protective material 32 to the surface of the photoreceptor is not limited to coating.

Next, the results of investigations by the present inventors on the appropriate amount of protective material required for protecting the photoreceptor surface will be described.
That is, first to third types of experiments described below were conducted to examine the deterioration state of the photoreceptor surface. All experiments were carried out in an experimental system composed of only the photosensitive member 1, the charging roller 2a, and the protective substance coating device 30 among the devices shown in FIG. From the study by the present inventors, it has become clear that the conditions for protecting the photoreceptor surface from deterioration due to proximity discharge are closely related to the charging conditions. The specific contents are described below. In addition, as the photoreceptor, one prepared by the following method was used.

[Photoreceptor 1]:
An undercoat layer coating solution, a charge generation layer coating solution, and a charge transport layer coating solution having the following composition are sequentially applied by dip coating on a φ30 aluminum cylinder and dried, and the film thickness is 4.5 μm. An undercoat layer, a 0.2 μm charge generation layer, and a 30 μm charge transport layer were formed.

[Undercoat layer coating solution]
Titanium dioxide powder 400 parts Melamine resin 65 parts Alkyd resin 120 parts 2-butanone 400 parts

[Coating liquid for charge generation layer]
Y-type oxotitanium phthalocyanine pigment 2 parts Polyvinyl butyral (ESREC BM-2: manufactured by Sekisui Chemical) 2 parts Tetrahydrofuran 50 parts

[Charge transport layer coating solution]
Bisphenol Z polycarbonate (Panlite TS-2050, manufactured by Teijin Chemicals) 10 parts Low molecular charge transport material having the structure shown in the following structural formula (1) 6 parts Tetrahydrofuran 100 parts

[First experiment]:
The peak-to-peak voltage value of the AC voltage applied to the charging roller 2a, that is, the amplitude Vpp of the AC component applied to the charging member is changed to 2.2 kV, 2.6 kV, and 3.0 kV, and the frequency f of the AC voltage is 1350 Hz. The DC voltage was -600V. The moving speed v of the surface of the photoreceptor is 113 mm / s. FIG. 5 shows the results of this experiment plotted with the change in Vpp applied to the charging member on the horizontal axis and the amount of film thickness reduction of the photosensitive member on the vertical axis.

As can be seen from FIG. 5, the amount of decrease in the photoreceptor film thickness is proportional to Vpp. Further, when Vpp is about 1.9 kV, the film thickness reduction is zero. The present inventors consider this point as follows.
It is known that when an AC voltage is applied, discharge does not start between the charging member surface and the photoreceptor surface unless the voltage applied to the charging roller 2a (charging member) exceeds a predetermined value. According to the studies by the present inventors, in the case of non-contact charging, the voltage applied to the charging member when the closest distance between the charging member surface and the photoreceptor surface is Gp μm is represented by the following formula (2). It has been found that discharge is started between the surface of the charging member and the surface of the photosensitive member when the value becomes equal to or greater than. Hereinafter, this value is referred to as a discharge start voltage Vth.
Vth = 312 + 6.2 × (d / εopc + Gp / εair) + (7737.6 × d / εopc) ^1/2 (2)

  In the above formula (2), d is the film pressure (μm) of the photoconductor, εopc is the relative dielectric constant of the photoconductor, Gp is the closest distance (μm) between the surface of the charging roller 2a (charging member) and the surface of the photoconductor. εair represents the relative dielectric constant in the space between the photoreceptor and the charging member. The unit of Vth is (V).

When the AC voltage Vpp is equal to or more than twice the above Vth, a bidirectional discharge occurs between the charging member and the photosensitive member.
In this example, the gap between the charging roller and the photosensitive member is 50 μm, the relative dielectric constant of the photosensitive member is about 3, the film thickness is 30 μm, and the relative dielectric constant in the space between the photosensitive member and the charging member is about 1. When applied to the above equation, Vth = 962 (V), and when the voltage applied to the charging member exceeds 962 (V), discharge is started between the charging member surface and the photoreceptor surface, and Vpp is about 1924 (V ) Is considered to start discharging by the AC voltage. The dominant discharge phenomenon is bi-directional discharge caused by the AC voltage. For this reason, it is considered that when the Vpp exceeds about 1.9 (kV), the photoconductor film thickness starts to decrease.

[Second experiment]:
The frequency f of the AC voltage applied to the charging roller was changed to 500 Hz, 900 Hz, 1400 Hz, 2000 Hz, and 4000 Hz, the peak-to-peak voltage value Vpp of the AC voltage was fixed at 2.2 kV, and the DC voltage was −600 V. The moving speed v of the photoreceptor surface was 104 mm / s. FIG. 6 shows the results of this experiment plotted with the change in frequency f on the horizontal axis and the film thickness reduction amount of the photoreceptor on the vertical axis.

As is apparent from FIG. 6, it can be seen that the amount of decrease in the photoreceptor film thickness is proportional to f. As described above, the decrease in the photosensitive member film thickness depends on the charging condition, and is specifically proportional to Vpp and f.
Accordingly, the present inventors have found that the decrease in the thickness of the photoreceptor is proportional to [Vpp− (2 × Vth)], is proportional to f, and is low per unit area even under the same charging condition when the moving speed of the photoreceptor is slow. Since the discharge energy to be irradiated is predicted to be large, it is predicted to be inversely proportional to the moving speed v of the photosensitive member surface.

[Third experiment]:
Based on the above results and predictions, experiments were conducted to determine the appropriate amount of protective material necessary to prevent deterioration of the photoreceptor surface due to discharge. Zinc stearate was used as a protective substance for determining the appropriate amount.
The moving speed v of the photoreceptor surface, the amplitude Vpp of the AC component applied to the charging member, the frequency f, the presence or absence of deterioration of the photoreceptor surface while changing the amount of the protective substance, the amount of zinc stearate present on the photoreceptor surface, In other words, the relationship between the amount of zinc stearate on the surface of the photoreceptor to be discharged measured by XPS was examined under normal temperature and humidity. The results are shown in Table 1 below.

In Table 1, X = [Vpp− (2 × Vth)] × (f / v), and the element ratio (%) of zinc stearate is measured by XPS of zinc stearate present on the surface of the photoreceptor. It is expressed by the element ratio of zinc (Zn).
Although it is very difficult to measure the amount of a small amount of protective substance present on the surface of the photoreceptor, the present inventors measured a characteristic element (for example, Zn in the case of zinc stearate) in the protective substance. As a result, the inventors have succeeded in obtaining knowledge about the abundance of protective substances required on the surface of the photoreceptor. For example, the element ratio (%) of zinc stearate was measured using a Quantum 2000 scanning X-ray electron spectrometer (XPS) manufactured by PHI under the conditions of an X-ray source AlKα and an analysis region of 100 μmφ.

  The element ratio of Zn is determined by first conducting an experiment with a voltage applied to the charging member to check for the presence of white turbidity and the amount of decrease in film thickness, and then image for 5 hours without applying voltage to the charging member. This is a value obtained when the forming apparatus is operated and zinc stearate is continuously applied, and the amount of zinc present on the surface of the photoreceptor is measured by XPS after 5 hours.

  Since zinc does not exist in the surface layer of the photoreceptor 1 used in this embodiment, that is, the charge transport layer, all Zn measured by XPS is derived from zinc stearate which is a protective substance. In that sense, Zn can be said to be a characteristic element representing the amount of the protective substance. Naturally, even when a protective substance other than zinc stearate is used, knowledge about the amount of the protective substance can be obtained if the protective substance contains a characteristic element that does not exist on the surface of the photoreceptor. it can.

From the results in Table 1, when the relationship between X and Zn is plotted to obtain a straight line representing the boundary of the presence or absence of cloudiness, the element ratio of Zn measured by XPS of zinc stearate on the surface of the photoreceptor in the discharged region ( %)), The following formula (4) is obtained, and the amount of zinc stearate necessary to prevent white turbidity due to deterioration and alteration of the surface of the photoreceptor is determined to be a value equal to or greater than formula (4).
1.52 × 10 ⁻⁴ × [Vpp− (2 × Vth)] × (f / v) (4)

In the above formula, Vpp is the amplitude (V) of the AC component applied to the charging member, f is the frequency (Hz) of the AC component applied to the charging member, and v is the moving speed (mm / mm) of the photosensitive member surface facing the charging member. sec), Vth represents the discharge start voltage (V).
Here, the value of Vth is as follows: the film pressure of the photoconductor is d (μm), the relative dielectric constant of the photoconductor is εopc, the closest distance (μm) between the surface of the charging member and the surface of the photoconductor is Gp, and the photoconductor is charged. When the relative dielectric constant in the space between the members is εair, the following formula (2):
Vth = 312 + 6.2 × (d / εopc + Gp / εair) + (7737.6 × d / εopc) ^1/2 (2)
Calculated from

Further, when the relationship between X and Zn is plotted from the results in Table 1 to obtain a straight line representing the boundary of whether or not the film thickness is reduced, the metal measured by XPS of zinc stearate on the surface of the photoreceptor in the discharged region is obtained. The following formula (5) is obtained as the amount of the element ratio (%), and the amount of zinc stearate necessary for almost no decrease in film thickness is determined to be a value equal to or greater than the formula (5).
2.22 × 10 ⁻⁴ × [Vpp− (2 × Vth)] × (f / v) (5)

In the above formula, Vpp is the amplitude (V) of the AC component applied to the charging member, f is the frequency (Hz) of the AC component applied to the charging member, and v is the moving speed (mm / mm) of the photosensitive member surface facing the charging member. sec), Vth represents the discharge start voltage (V).
Here, the value of Vth is as follows: the film pressure of the photoconductor is d (μm), the relative dielectric constant of the photoconductor is εopc, the closest distance (μm) between the surface of the charging member and the surface of the photoconductor is Gp, and the photoconductor is charged. When the relative dielectric constant in the space between the members is εair, the following formula (2):
Vth = 312 + 6.2 × (d / εopc + Gp / εair) + (7737.6 × d / εopc) ^1/2 (2)
Calculated from
FIG. 7 shows the relationship between X described above and the element ratio (%) of Zn.

Based on the element ratio of Zn obtained as described above, an appropriate amount of the protective substance present on the surface of the photoreceptor in the region to be discharged can be obtained. That is, based on the measurement result, the amount of the total element ratio (%) measured by XPS of the protective substance can be set as follows.
Considering that the molecular formula of zinc stearate is [CH ₃ (CH ₂ ) ₁₆ COO] ₂ Zn, there are 36 C, 4 O, and 70 H for 1 Zn. . Among these, since H is not detected by XPS, the total element ratio of zinc stearate detected by XPS is 41 times the element ratio of Zn.

That is, the total element ratio (%) measured by XPS of the protective substance based on the above formula (4) indicating the amount of the element ratio (%) of the metal obtained in the straight line representing the boundary of the presence or absence of cloudiness described above. When the amount of is calculated, the following formula (1) is obtained, and the amount of the protective substance necessary for preventing white turbidity due to deterioration and alteration of the surface of the photoreceptor can be set to a value that is equal to or greater than the formula (1).
6.23 × 10 ⁻³ × [Vpp− (2 × Vth)] × (f / v) (1)

In the above formula, Vpp is the amplitude (V) of the AC component applied to the charging member, f is the frequency (Hz) of the AC component applied to the charging member, and v is the moving speed (mm / mm) of the photosensitive member surface facing the charging member. sec), Vth represents the discharge start voltage (V).
Here, the value of Vth is as follows: the film pressure of the photoconductor is d (μm), the relative dielectric constant of the photoconductor is εopc, the closest distance (μm) between the surface of the charging member and the surface of the photoconductor is Gp, and the photoconductor is charged. When the relative dielectric constant in the space between the members is εair, the following formula (2):
Vth = 312 + 6.2 × (d / εopc + Gp / εair) + (7737.6 × d / εopc) ^1/2 (2)
Calculated from

Further, based on the above formula (5) indicating the amount of the element ratio (%) of the metal obtained in the straight line representing the boundary of whether or not the film thickness is reduced, the ratio of all elements measured by XPS of the protective substance ( %) Is obtained, the following formula (3) is obtained, and the amount of protective material required for the amount of protective material necessary for almost no decrease in the film thickness on the surface of the photoreceptor is appropriate. Can be set.
9.10 × 10 ⁻³ × [Vpp− (2 × Vth)] × (f / v) (3)

In the above formula, Vpp is the amplitude (V) of the AC component applied to the charging member, f is the frequency (Hz) of the AC component applied to the charging member, and v is the moving speed (mm / mm) of the photosensitive member surface facing the charging member. sec), Vth represents the discharge start voltage (V).
Here, the value of Vth is as follows: the film pressure of the photoconductor is d (μm), the relative dielectric constant of the photoconductor is εopc, the closest distance (μm) between the surface of the charging member and the surface of the photoconductor is Gp, and the photoconductor is charged. When the relative dielectric constant in the space between the members is εair, the following formula (2):
Vth = 312 + 6.2 × (d / εopc + Gp / εair) + (7737.6 × d / εopc) ^1/2 (2)
Calculated from

  The reason why the surface of the photoreceptor can be protected from deterioration due to the proximity discharge depending on the amount of zinc stearate can be considered as follows. When the photosensitive member 1 is charged by proximity discharge, the surface of the photosensitive member is irradiated with energy of particles (for example, electrons, excited molecules, ions, plasma, etc.) generated by the discharge in the discharge region of the photosensitive member surface. This energy is resonated and absorbed by the binding energy of the resin molecules in the charge transport layer that composes the surface of the photoconductor, and the molecular weight is lowered by cutting the resin molecular chains, resulting in a decrease in the degree of entanglement of the polymer chains. It is thought that the film thickness is reduced due to deterioration.

  On the other hand, if a protective substance is present on the surface of the photoreceptor, it is the protective substance that is directly irradiated with the energy of the particles generated by the discharge, so that the photoreceptor itself is free from direct irradiation of the particles generated by the discharge. Therefore, it is considered that the protective substance itself absorbs the energy of the particles generated by the discharge and alleviates chemical deterioration of the surface of the photoreceptor.

  Also in the experiment, for example, in a region where there is no protective substance on the surface of the photoconductor (referred to as region B), the surface of the photoconductor is protected from the analysis of molecular debris constituting the photoconductor. In the region where the substance exists (referred to as region A), the debris of the molecules constituting the photoconductor was not detected, and the photoconductor surface under the protective material was not deteriorated. And in this area | region A, the substance which the zinc stearate supplied as a protective substance changed chemically and decomposed | disassembled was detected.

  In the image forming apparatus of the present embodiment, zinc stearate is used as the protective substance 32. However, zinc stearate is an example of the protective substance, and other substances such as various fatty acid salts, waxes, silicone oils, and the like are protective substances. The object of the present invention can be achieved by maintaining an appropriate amount of the protective substance determined by the above examination.

  Among the fatty acid salts, the fatty acid metal salt is easily a characteristic element in which the metal element is measured by XPS, and is easy to measure when setting conditions such as the coating amount. Therefore, it is suitable for designing an apparatus for supplying an optimum amount of a protective substance to the surface of the photosensitive member according to the charging conditions as in this embodiment.

  Examples of fatty acids include undecyl acid, lauric acid, tridecyl acid, myristic acid, palmitic acid, pendadecyl acid, stearic acid, heptadecyl acid, arachidic acid, montanic acid, oleic acid, arachidonic acid, caprylic acid, capric acid, caproic acid, etc. Examples of the metal salt include salts with metals such as zinc, iron, copper, magnesium, aluminum, and calcium.

  Furthermore, it is desirable to use a lamellar crystal powder such as zinc stearate as a protective substance. A lamellar crystal has a layered structure in which amphiphilic molecules are self-organized, and when a shearing force is applied, the crystal breaks along the layers and is slippery. This action is effective in reducing the coefficient of friction, and is advantageous when viewed from the viewpoint of protecting the photoreceptor surface from discharge. For example, the characteristic of lamellar crystals that uniformly cover the surface of the photoreceptor under shearing force is desirable as a protective substance because the surface of the photoreceptor can be effectively covered with a small amount of protective substance.

  In order to fully protect the surface of the photoreceptor from electric discharge by fully utilizing the properties of the lamella crystals, the protective material coating device 30 applies a shearing force so as to have a linear velocity difference from the surface of the photoreceptor 1. However, it is desirable to apply and supply a protective substance. That is, it is preferable to operate the photosensitive member so that the linear velocity of movement of the photosensitive member and the linear velocity of movement of the protective substance coating device in contact with the photosensitive member are different.

  In addition, when the object is to protect the surface of the photoreceptor from deterioration due to electric discharge as in the present invention, it is desirable that the protective substance coating device 30 is provided between the cleaning device 8 and the charging device 2. This is to prevent the protective material from being removed by the cleaning device before reaching the discharge region.

  Here, the image forming apparatus of the present embodiment includes a temperature / humidity detector (not shown) for detecting the environment around the charging roller. Further, the image forming apparatus according to the present embodiment includes a first table that associates the rotation speed of the fur brush with the amount of the protective substance supplied to the surface of the photosensitive member, and a temperature / humidity detector in a controller (not shown). According to the charging condition, the second table that matches the detected environment around the charging roller and the charging condition, the application control unit that controls the rotation speed of the fur brush, the charging control unit that controls the charging condition, A computer for calculating the amount of the protective member required is included.

  More specifically, the first table has a table in which the rotation speed of the fur brush is associated with the element ratio of Zn obtained as a result of the measurement by XPS. Also, the second table shows the temperature and humidity values and the Vpp value necessary for the discharge in order to reliably generate an AC voltage discharge even when the discharge start voltage changes due to the environment around the charging roller. It is a corresponding table.

  Further, in order to calculate the necessary amount of the protective member according to the charging condition, the computer calculates the required element ratio of zinc stearate from the above formula (4) or the above formula (5) from the charging condition.

  In such a configuration, when an image formation start command is input, the image forming apparatus of the present embodiment first detects the environmental conditions of temperature and humidity by the temperature / humidity detector, and then detects the second temperature from the detected temperature and humidity. The Vpp value of the charging condition is obtained from the table, the necessary Zn element ratio is calculated by the computer based on the charging condition, and the rotation speed of the fur brush is obtained from the first table based on the calculated Zn element ratio. The application control unit rotates the fur brush at an optimum rotation speed according to the Vpp value of the charging condition thus obtained, and the charging control unit starts charging while controlling the voltage applied to the charging member.

By such control, even when the charging condition changes according to the environment, it is possible to supply the optimum protective substance to the surface of the photoconductor to prevent the photoconductor from being deteriorated.
When calculating the necessary element ratio of zinc stearate according to the above formula (4) or formula (5), it is necessary to calculate Vth in consideration of the decrease in the film thickness of the photoreceptor. There is. Therefore, the controller further has a storage means for storing the accumulated discharge time and a third table for deriving the film thickness of the photoreceptor from the accumulated discharge time, and the photoreceptor film corresponding to the accumulated discharge time by the third table. The thickness is derived and Vth is calculated.

As described in Embodiment 1 above, based on the amount of the total element ratio (%) measured by XPS of the protective material present on the surface of the photoconductor in the proximity-discharged region, the abundance is appropriately maintained. By doing so, the surface of the photoreceptor is protected to prevent deterioration, and a lubricating action is also suitably imparted. In particular, the effect is more remarkable when the cycle time is less than 0.60 seconds / cycle, preferably less than 0.44 seconds / cycle.
Although the details of the reason for the conspicuous effect appearing are unclear, contact between the outer diameter of the photoconductor cylinder having a curvature and the contact member, and contact caused by resonance between the contact member and the photoconductor cylinder due to process operation It is considered that the malfunction of the member function becomes conspicuous when the cycle time is less than 0.60 sec / cycle, and further less than 0.44 sec / cycle. Here, the malfunction of the contact member function includes, for example, chatter, abnormal noise, blade reversal, and the like. It has been found that by adopting the configuration of the present invention, these problems can be prevented very effectively.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to a following example.

  Using the image forming apparatus having the main configuration shown in FIG. 3 of [Embodiment 1] and the photoconductor 1 having the configuration described in the first to third experiments, the moving speed of the photoconductor surface, the cycle time, Experiments were performed by changing the frequency f of the AC voltage and the coating amount of the protective substance, and the torque of the photoconductor, the wear amount, and the state of the cleaning blade edge after running 40,000 sheets were evaluated. The experimental conditions are shown below.

<Experimental equipment>
The photoreceptor 1 was mounted on a process cartridge for an electrophotographic apparatus and set in a modified Ricoh digital copying machine Imagio Neo 270 equipped with a semiconductor laser having an image exposure light source wavelength of 780 nm. As shown in FIG. 3, the process cartridge provided with the protective substance applying device fixes a fur brush as a protective substance applying member so that the brush end is in contact with the surface of the photosensitive member, and further zinc stearate is attached to the photosensitive member. The bar-shaped protective substance solid material melted and solidified to fit the length is fixed so that it also contacts the brush end of the fur brush, and the fur brush rotates to supply the protective substance to the photoreceptor surface. Remodeled as follows. At that time, the presence or absence of contact between the fur brush and the protective substance solid material can be arbitrarily controlled, thereby controlling the coating amount of the protective substance.

<Setting conditions>
A gap tape with a film thickness of 50 μm was attached to both ends of the charging roller so that the charging roller and the photosensitive member were not in contact with each other, and an alternating voltage in which an AC voltage was superimposed on a DC voltage was applied. The peak-to-peak voltage Vpp of the AC voltage applied to the charging member was set to 2200V, the frequency f, the moving speed of the photosensitive member, the DC voltage was set to -750V, and the developing bias was set to -500V. The amount of laser light was set according to the photosensitive member moving speed so that the potential after exposure was -130V.
As shown in Table 2, the setting conditions in the evaluation are represented by the photosensitive element moving speed, the cycle time required for printing, the frequency f of the AC voltage, and the element ratio (%) of Zn in zinc stearate measured by XPS. The amount of the protective substance applied was changed to 1-8.

<Evaluation experiment: (Examples 1-8)>
First, after the photosensitive member 1 is mounted on the process cartridge, a letter image having a printing rate of about 5% in a temperature / humidity environment of 30 ° C./85% RH is obtained with a modified Imagio Neo 270 machine under the conditions 1 to 8 set above. 40,000 A4 sheets were printed continuously. After printing 40,000 sheets, the photoconductor was taken out from the process cartridge, and the wear amount of the photoconductor and the state of the cleaning blade edge were confirmed. The photoreceptor wear was measured with an eddy current film thickness meter manufactured by Fischerscope. The results are shown in Table 3 below.
<Evaluation criteria in the table>
○: No abnormality, △: Minor blade missing, ×: Blade missing, XX: Evaluation stopped due to blade turning before reaching 40,000 sheets

  Also, remove the charging roller, which is a part that charges the photoconductor, from the cleaner unit of the process cartridge, and attach it to a device that can measure the rotational torque of the photoconductor of this cleaner unit with the cleaning blade in contact with the photoconductor. The rotational torque of the drum was measured under the above set conditions in an environment of 30 ° C./85% RH. The rotational torque was measured for the initial photoconductor after printing 40,000 sheets, and the value after 1 minute drive was measured and evaluated. The rotation axis of the photoconductor is an axis that penetrates the center of the cylinder, like the photoconductor through-axis of the cleaner unit. The results are shown in Table 3 below.

<Evaluation experiment: (Comparative Examples 1-4)>
In Examples 1, 3, 5, and 7 above, the torque, wear amount, and 40,000 sheet run of the photoconductor were the same as in Examples 1, 3, 5, and 7 except that no protective material was applied as a setting condition. The subsequent cleaning blade edge condition was evaluated. The results are shown in Table 3 below.

<Evaluation Experiment: (Comparative Examples 5 to 8)>
In Examples 1, 3, 5 and 7, C-type polyarylate resin (weight average molecular weight) was used instead of 10 parts of bisphenol Z polycarbonate (Panlite TS-2050: manufactured by Teijin Chemicals) used in the charge transport layer coating solution. Examples 1, 3, and 5 except that 8 parts of Mw = 110,000) and 2 parts of polycarbonate resin copolymerized with a siloxane unit represented by the following structural formula (2) were used, and no protective material was applied as a setting condition. In the same manner as in No. 7 and No. 7, the torque of the photoconductor, the wear amount, and the cleaning blade edge state after 40,000 sheets of run were evaluated. The results are shown in Table 3 below.

  As is clear from the above results, when the image forming apparatus and the process cartridge for the image forming apparatus of the present invention are used, deterioration and deterioration of the surface of the photoreceptor due to proximity discharge is prevented, and a high-speed process and a small cycle time are achieved. Also, the amount of wear of the photoconductor is small without increasing the photoconductor torque, and the blade is hardly damaged. As a result, it is possible to form a stable image with good durability and without the occurrence of blade reversal or abnormal image.

6 is a graph showing the relationship between the run time and the amount of film scraping on the surface of the photoconductor when a charging experiment is continuously performed for about 150 hours with the charging member placed close to the surface of the photoconductor in a non-contact state. FIG. 4 is a schematic diagram for explaining an initial surface state (a) and a deteriorated state (b) of the photosensitive member 1 when the charging roller 2a and the surface of the photosensitive member are opposed to each other with a minute gap and are subjected to proximity discharge. 1 is a schematic configuration diagram illustrating an example of an image forming apparatus applied in Embodiment 1 and Examples of the present invention. 1 is a schematic configuration diagram illustrating an example of a charging device 2 used in an image forming apparatus applied in Embodiment 1 and Examples of the present invention. 6 is a graph showing the relationship between the change in Vpp applied to the charging member obtained from the first experiment in Embodiment 1 of the present invention and the amount of film thickness reduction of the photoreceptor. 6 is a graph showing the relationship between the frequency f of the AC voltage applied to the charging roller obtained from the second experiment in Embodiment 1 of the present invention and the film thickness reduction amount of the photoreceptor. It is a graph which shows the relationship of the element ratio of X and Zn obtained from the 3rd experiment in Embodiment 1 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photoconductor 2 Charging apparatus 2a Charging roller 3 Exposure apparatus 4 Developing apparatus 5 Transfer apparatus 6 Fixing apparatus 8 Cleaning apparatus 9 Static eliminating apparatus 10 Transfer material conveyance path 30 Protective substance application apparatus 31 Far brush 32 Protective substance 33 Pressure spring

Claims (4)

A photosensitive member that moves, a protective substance coating device that supplies a protective substance while abutting and moving on the surface of the photosensitive member, and a discharge that is caused by application of a voltage that includes an alternating current component that is disposed in contact with or close to the photosensitive member At least a charging device including a charging member for charging the photosensitive member, an exposure device for forming an electrostatic latent image on the surface of the charged photosensitive member, and a developing device for developing the formed electrostatic latent image with toner. An image forming apparatus comprising:
The photoreceptor includes a photosensitive layer in which a charge transport layer and a charge generation layer are laminated in order from the surface side,
The charge transport layer comprises polycarbonate;
The protective substance is zinc stearate, and the amount of metal element ratio (%) measured by XPS of the fatty acid metal salt present on the surface of the photoreceptor in the discharged region is represented by the following formula (4):
1.52 × 10 ⁻⁴ × [Vpp− (2 × Vth)] × (f / v) (4)
(Wherein, Vpp is the amplitude (V) of the AC component applied to the charging member, f is the frequency (Hz) of the AC component applied to the charging member, and v is the moving speed (mm / mm) of the photosensitive member surface facing the charging member. sec), Vth represents the discharge start voltage (V), Vpp satisfies 2200 ≦ Vpp ≦ 3000, and f satisfies 500 ≦ f ≦ 4000.
Here, the value of Vth is as follows: the film thickness of the photoconductor is d (μm), the relative dielectric constant of the photoconductor is εopc, the closest distance (μm) between the charging member surface and the surface of the photoconductor is Gp, and the photoconductor is charged. When the relative dielectric constant in the space between the members is εair, the following formula (2):
Vth = 312 + 6.2 × (d / εopc + Gp / εair) + (7737.6 × d / εopc) ^1/2 (2)
Calculated from )
An image forming apparatus characterized in that the cycle time required for printing on the photosensitive member is less than 0.60 seconds / cycle. The amount of the metal element ratio (%) measured by XPS of the fatty acid metal salt present on the surface of the photoreceptor in the discharged region is represented by the following formula (5):
2.22 × 10 ⁻⁴ × [Vpp− (2 × Vth)] × (f / v) (5)
(Wherein, Vpp is the amplitude (V) of the AC component applied to the charging member, f is the frequency (Hz) of the AC component applied to the charging member, and v is the moving speed (mm / mm) of the photosensitive member surface facing the charging member. sec), Vth represents the discharge start voltage (V).
Here, the value of Vth is as follows: the film thickness of the photoconductor is d (μm), the relative dielectric constant of the photoconductor is εopc, the closest distance (μm) between the charging member surface and the surface of the photoconductor is Gp, and the photoconductor is charged. When the relative dielectric constant in the space between the members is εair, the following formula (2):
Vth = 312 + 6.2 × (d / εopc + Gp / εair) + (7737.6 × d / εopc) ^1/2 (2)
Calculated from )
The image forming apparatus according to claim 1, wherein the image forming apparatus is equal to or greater than an amount obtained according to claim 1.   The image forming apparatus according to claim 1, wherein a cycle time required for the printing is less than 0.44 seconds / cycle. The image forming apparatus according to claim 1, wherein a linear movement speed of the photosensitive member is different from a linear movement speed of a protective material coating device that contacts the photosensitive member.

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